[LRUCache] Expose LRU Cache status to metrics

[acelyc111]

Proposed changes

Expose LRU Cache status to metrics would be helpful to diagnose
problems like high usage, low hit rate.

Types of changes

What types of changes does your code introduce to Doris?
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• [] Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [] Documentation Update (if none of the other choices apply)
• [] Code refactor (Modify the code structure, format the code, etc...)

Checklist

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• [] I have create an issue on (Fix #ISSUE), and have described the bug/feature there in detail
• Compiling and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• [] If this change need a document change, I have updated the document
• [] Any dependent changes have been merged

[morningman]

Hi @acelyc111 , thanks for your PR.
And I suggest to add document for new API. Better to place it here:
administrator-guide/http-actions/be/lru-cache-action.md.

You can refer to the content format in administrator-guide/http-actions/fe/connection-action.md

[acelyc111]

Please review #4751 at first

[acelyc111]

Hi @acelyc111 , thanks for your PR.
And I suggest to add document for new API. Better to place it here:
administrator-guide/http-actions/be/lru-cache-action.md.

You can refer to the content format in administrator-guide/http-actions/fe/connection-action.md

@morningman I've change to expose these status to metric instead of http API, metric is more firendly to third-party monitor system.

[morningman]

LGTM